Besoin d'aide pour corriger W3C

Bonjour à tous,

J'ai fait un site avec Joomla et lorsque j'ai voulu le valider avec W3C il y a une cinquantaine d'erreurs.
exemple :

Line 56, Column 99: required attribute "alt" not specified
...><img src="/templates/bestcars-tg/images/logo.png" border="0" class="logo"></a>
?
The attribute given above is required for an element that you've used, but you have omitted it. For instance, in most HTML and XHTML document types the "type" attribute is required on the "script" element and the "alt" attribute is required for the "img" element.

Typical values for type are type="text/css" for <style> and type="text/javascript" for <script>.

Error Line 56, Column 103: end tag for "img" omitted, but OMITTAG NO was specified
...><img src="/templates/bestcars-tg/images/logo.png" border="0" class="logo"></a>
?
You may have neglected to close an element, or perhaps you meant to "self-close" an element, that is, ending it with "/>" instead of ">".

Info Line 56, Column 26: start tag was here
            	<a href="/"><img src="/templates/bestcars-tg/images/logo.png" bord...
Error Line 844, Column 158: required attribute "type" not specified
.../connect.facebook.net/fr_FR/all.js#appId=582735905073815&amp;xfbml=1"></script>
?
The attribute given above is required for an element that you've used, but you have omitted it. For instance, in most HTML and XHTML document types the "type" attribute is required on the "script" element and the "alt" attribute is required for the "img" element.

Typical values for type are type="text/css" for <style> and type="text/javascript" for <script>.

Mais je ne sais pas ou il faut aller pour trouver les lignes et les colonnes pour corriger ces erreurs. Si quelqu'un pouvait m'aider.
Merci